Surgical sutures and attached surgical needles are well known in the art for use in a variety of conventional surgical procedures. For example, such sutures may be used to approximate tissue about incisions or lacerations in epidermal layers and underlying fascia layers, join blood vessel ends, attach tissue to medical devices such as heart valves, repair body organs, repair connective tissue, etc. Conventional surgical sutures may be made from known biocompatible materials, particularly synthetic and natural biocompatible polymeric materials, which may be non-absorbable or absorbable. Examples of synthetic non-absorbable polymeric materials useful to manufacture non-absorbable sutures include polyesters, polyolefins, polyvinylidene fluorides and polyamides. Examples of synthetic absorbable polymeric materials useful to manufacture absorbable sutures include polymers and copolymers made from lactones such as the lactides, glycolide, p-dioxanone, ε-caprolactone, and trimethylene carbonate. The term absorbable is meant to be a generic term, which may also include bioabsorbable, resorbable, bioresorbable, degradable or biodegradable.
Absorbable sutures are preferred by surgeons for use in many surgical procedures because of several advantages and properties possessed by such sutures. Absorbable sutures must be capable of providing the desired tensile strength in vivo for a sufficient period of time to allow for effective tissue healing. Wound healing is dependent on the nature of the specific tissue as well as the healing characteristics of the individual undergoing the surgical procedure. For example, poorly vascularized tissue is likely to heal more slowly than highly vascularized tissue; likewise, diabetic patients and the elderly tend to heal more slowly as well. There are thus opportunities to provide suture materials that can match the healing characteristics of a variety of wounds. Any implant, such as a suture, appears as a foreign body to the patient's immune system. Upon absorption of an absorbable suture the polymeric material comprising the suture is eliminated from the body, thus providing, it is believed, a better patient outcome. The outcome may be improved for several reasons including decreased post-operative pain, reduced risk of long-term infections, and better patient comfort. In addition, it is known that implantable medical devices, including sutures, may provide a platform for the attachment of bacteria and the subsequent formation of bacterial biofilms. The absorption and elimination of absorbable sutures may result in a significant diminishment of infections and decreased biofilm formation at the wound site.
Absorbable sutures may be manufactured as monofilament sutures or as braided multifilament sutures. Monofilament sutures are of particular interest because of several advantageous properties, including less infection potentiation, better knot sliding, less tissue drag and, in general, less tissue reactions attributable to overall smaller surface area. Multifilament sutures have associated advantages as well including flexibility or hand, and knot security characteristics. Multifilament sutures may have disadvantages in certain aspects of their use. One particular perceived disadvantage of a braided multifilament suture is the tendency to wick fluids along the length of the suture. This is believed by some to be attributable to the presence of interstices between the braided filaments that create a fluid pathway. This fluid pathway may allow bacteria to readily travel with fluids along the length of the suture as fluids are wicked along this fluid pathway with the possibility of an infection moving along the length of implanted suture at the tissue repair site. Another disadvantage is that multifilament sutures must be braided from smaller diameter fibers, adding another manufacturing step.
It is to be understood that if an absorbable polymer can be made into a successful multifilament suture, it may not necessarily be made into a successful monofilament suture. Monofilament sutures must be based upon polymers that exhibit an inherent softness; this characteristic is often reflected in a low glass transition temperature (Tg). Thus a very successful multifilament suture based on 10/90 poly((L-)-lactide-co-glycolide) would not generally make a successful monofilament suture because this copolymer has a glass transition temperature above room temperature, rendering monofilament fibers of any substantial diameter quite stiff.
Another important aspect of an absorbable polymer, if it is to be made into a monofilament suture, is the need for it to be dimensionally stable. Thus, as the molecular orientation of the polymer is increased during fiber processing to increase strength, the driving force to shrink and deform is increased. This is particularly problematic with low glass transition temperature polymers used to make monofilament sutures. Dimensional stability is provided to the suture by virtue of the rapid crystallization of the polymer during fiber formation. Accordingly, the highly oriented polymer of a strong monofilament suture is prevented from shrinking or deforming due to the presence of this morphological characteristic—sufficient crystallinity.
Absorbable sutures are designed to have the requisite physical characteristics to assure desirable and efficacious in vivo behavior. Specifically, the sutures need appropriate tensile strength during the required healing period; this is typically characterized as breaking strength retention. As the advantages of absorbable sutures continue to become more recognized and accepted, there is a need for sutures having different breaking strength retention profiles that are matched to the differing tissue requirements presented in a variety of surgical procedures. In order to obtain the required design properties, it is necessary to provide absorbable polymers and manufacturing processes that will yield absorbable sutures with the required properties.
The retention of mechanical properties post-implantation is often a very important and critical feature of an absorbable medical device. The device must retain mechanical integrity until the tissue has healed sufficiently. In some bodily tissues, healing occurs more slowly, requiring an extended retention of mechanical integrity. As mentioned earlier, this is often associated with tissue that has poor vascularization. Likewise there are other situations in which a given patient may be prone to poor healing, e.g., the diabetic patient. There are, however, many situations in which rapid healing occurs, which require the use of fast absorbing medical devices such as sutures; this is often associated with excellent vascularization. Examples of instances where such fast absorbing sutures can be used include, but are not limited to, certain pediatric surgeries, oral surgery, repair of the peritoneum after an episiotomy, and superficial wound closures.
When rapid healing occurs, the mechanical retention profile of the medical device could reflect a more rapid loss in properties. Concomitant with this is the rate of absorption (bioabsorption or resorption), that is, the time required for the medical device to disappear from the surgical site.
Absorbable polymers for use in absorbable sutures and manufacturing processes for such sutures have been disclosed in the art in order to provide improved absorbable sutures.
Bezwada, et al. in U.S. Pat. No. 4,653,497 describes crystalline p-dioxanone and glycolide copolymers and surgical devices therefrom.
The problem of slow crystallization rates in glycolide-containing copolymers was addressed in U.S. Pat. No. 6,794,484 and U.S. Pat. No. 6,831,149. These patents disclose the use of specific ratios of mono- to difunctional initiators to generate copolymers that have significantly faster nucleation rates compared to copolymers made from either monofunctional or difunctional initiators alone. Among other glycolide containing copolymer compositions, a 92/8 poly(p-dioxanone-co-glycolide) (PDO/Gly) copolymer prepared from dodecanol and diethylene glycol in a molar ratio of 50:50 was described. Medical devices including sutures made from such copolymers were disclosed.
U.S. Pat. No. 8,262,963 discloses a process for making absorbable filaments from copolymers of glycolide and an alkylene carbonate such as trimethylene carbonate.
U.S. Pub. No. U.S. 2007/0035061 discloses a method of making absorbable microtubes from bioabsorbable polymers and copolymers.
Although existing absorbable sutures are adequate for their use in certain surgical procedures, there is a need in this art for novel surgical sutures having improved properties, in particular absorbable monofilament sutures that provide high tensile strength with lower Young's modulus, breaking strength retention (BSR) suitable for mid-term surgical applications, excellent knot sliding and knot security behavior, while still possessing good pliability/handling properties.
The need in this art for novel absorbable monofilament sutures exhibiting a breaking strength retention (BSR) suitable for mid-term surgical applications will now be addressed. There exist monofilament sutures, exemplified by MONOCRYL™ suture which is commercially available from Ethicon, Inc. (Somerville, N.J.), which lose their strength in a rather short time frame, approximately three weeks. There are many surgical repairs that heal within this timeframe and this is a very useful product class. For tissue that requires a very long time to heal, however, extended wound healing support must be provided. For very long fixation needs, a monofilament based on poly(p-dioxanone) homopolymer is commercially available, PDS II™ suture (Ethicon, Inc., Somerville, N.J.). This product loses all of its tensile strength between about 14 and 16 weeks post-implantation for suture sizes 4/0 to 2/0. What does not presently exist is a monofilament suture possessing a mid-term BSR profile in which all strength is lost between about 4 weeks and about 10 weeks, post-implantation. Novel sutures having these properties are desired to address these needs.
Also, there is a need for novel processes for making such novel monofilaments sutures. Such sutures would be useful in both existing surgical procedures where absorbable sutures are used, and would also be indicated for other surgical procedures and in patients where conventional absorbable sutures are less desirable. These surgical situations include slow-to-heal tissues, immune compromised patients, diabetic patients, and geriatric patients.